Optical waveguides – With disengagable mechanical connector – Optical fiber to a nonfiber optical device connector
Reexamination Certificate
1999-08-18
2001-11-06
Sugarman, Scott J. (Department: 2873)
Optical waveguides
With disengagable mechanical connector
Optical fiber to a nonfiber optical device connector
Reexamination Certificate
active
06312166
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to a laser diode array. More specifically, the present invention relates to a laser diode array having integral structures that facilitate the measurement of optical power generated by the laser diode array.
Laser diodes degrade with time and use. Therefore, the current supplied to the laser diode to produce a predetermined optical power at the beginning of life of the laser diode will be different from the current needed to produce the same predetermined optical power at the end of the effective life, i.e., just prior to failure, of that laser diode. It will be appreciated that this fact gives rise to the need to recalibrate the Power vs. Current curve and subsequently control these parameters over the operating life of the laser diode array. This laser diode aging problem is exacerbated when the device being controlled is not a single laser diode but a laser diode array constructed from many laser diode bars, each laser diode bar including a plurality of distinct laser diodes. If one bar fails, then the array continues to operate but at a reduced output level, which could adversely affect the quality of the product being manufactured with the laser.
Moreover, it is often desirable to be able to directly monitor various performance parameters of a laser diode array or system. These performance parameters can include, but are not limited to:
(i) power output;
(ii) optical activity or output;
(iii) wavelength detection and tuning indications;
(iv) laser operation data of the pumped laser using light traveling back from the laser medium in the cavity to the diode pump source;
(v) pulse output characteristics of pulse-driven diode pump sources; and
(vi) feedback from damaged optical fiber links for detection and diagnostic purposes.
Coupling optics have been used for coupling output emissions of a laser diode pump source to an optical fiber. An example of such coupling optics is disclosed in U.S. Pat. No. 5,127,068 (hereinafter the '068 patent), which is incorporated herein by reference. In the '068 patent, radiation emitted from a laser diode bar, constructed from a plurality of emitters, is focused into a corresponding number of multi-mode optical fibers by means of coupling optics placed between the emitting facets of respective emitters and the ends of the multi-mode optical fibers. The coupling optics disclosed in the '068 patent is simply a piece of the same multi-mode optical fiber, a strand of which extends along the length of a diode bar pump source. It will be appreciated that the coupling optics must be carefully positioned with respect to the emitter facets of the laser diode bar in order to properly collimate the emitter outputs. This is accomplished by aligning and securing the coupling optics in place with a suitable epoxy material.
Diagnosis of the performance characteristics for the system discussed immediately above are generally achieved by placing a beam sampling device, e.g., a beam splitter, in the path of the emitted light between any two of the diode pump source, the coupling optics, and the optical fiber. This diagnostic technique presents at least three problems:
(i) a beam sampler significantly increases the size of the package;
(ii) a beam sampler placed in the path of the emitted light attenuates a portion of the available light, which might otherwise be delivered; and
(iii) a beam sampler increases the cost of the system.
Moreover, even if the problem of limited space in the laser diode system were ignored, building a feedback subsystem for such a system would require extra mechanical components for stability. Such stabilizing elements add complexity to the feedback system as well as increase the weight and cost of the overall system.
In an attempt to overcome the problems mentioned above, U.S. Pat. No. 5,504,762 (hereinafter the '762 patent), which is also incorporated herein by reference, proposed employing the optical fiber constituting the coupling optics to conduct stray radiation, which is not included in the beam that is generated in the emission path by small imperfections in the surface of the lens, to an alternate location. The optical fiber, having a first end and a second end, is oriented with respect to the coupling optics such that radiation from the emitter region is optically coupled into the optical fiber. The second end of the optical fiber is coupled to the laser cavity. A detector is positioned in a spaced, adjacent relationship to the coupling optics, i.e., in an emission path of the stray radiation. The detector detects at least a portion of the stray radiation, and produces a detected output in response to the stray radiation.
More specifically,
FIG. 1
discloses an arrangement for coupling the radiation emitted from laser diode source
10
, which has a single emitter region, or a bar, having a plurality of emitters
20
,
22
and
24
, into multi-mode optical fibers
26
,
28
and
30
, which fibers are part of an optical fiber bundle
32
. The arrangement includes a coupling optics
18
disposed between the emitter facets of emitters
20
,
22
and
24
, and the ends of multi-mode optical fibers
26
,
28
and
30
. It will be noted that it is not necessary to couple a certain number of laser diode emitters to an equal number of fibers, fiber bundles, or other optical transfer elements. It is possible to overlay power from more than one emitter to a smaller number of fibers, fiber bundles, or optical transfer elements. It will also be noted that optical transfer devices can extend beyond fibers and can be substantially any optical device or media, either reflective, refractive or open media which is placed at the output of laser diode source
10
to allow the output to be effectively coupled to a desired application. Air is only one of many transfer elements. Other suitable transfer elements include fluids, liquids, and solids.
It should be mentioned that a spacing of approximately 60 microns from the near edge of coupling optics
18
to the diode facet is satisfactory for a 250-micron diameter fiber that has an index of refraction of 1.5. The optical spacing of the optical fiber end from coupling optics
18
should be as small as possible; a spacing of about 20 microns is acceptable.
It will be noted that the diameter of coupling optics
18
is chosen to be roughly equal to the diameter of the optical fiber to be coupled. The diameter of coupling optics
18
may be less than the diameter of the optical fiber to be coupled without loss in coupling efficiency. However, if such small coupling optics
18
diameters are used, the alignment of coupling optics
18
is more difficult. Coupling optics
18
is placed with respect to the output facets of laser diode source
10
in order to properly collimate them. This may be accomplished by carefully aligning coupling optics
18
and securing it in place with a suitable epoxy.
The NA of the optical fiber to be coupled is roughly equal to the low NA direction of diode source
10
, typically 0.1 to 0.15. This combination of coupling optics
18
and optical fiber results in a percentage greater than 80% coupling of the laser diode emitted energy into the multi-mode optical fiber. Coupling optics
18
and the butt-coupled end of the fiber have an anti-reflection coating to reduce reflections from these surfaces.
It will be noted that coupling optics
18
is cylindrical in cross-section. Those of ordinary skill in the art will recognize, however, that other cross-sectional shapes, including but not limited to, elliptical and hyperbolic, which can be useful for correction of particular spherical aberrations as known in the art, i.e., Kingslake,
Lens Design Fundamentals,
Academic Press, 1978.
As illustrated in
FIG. 1
, the optical fibers
26
,
28
and
30
are rectangular in cross-section in order to reduce the total amount of glass in the fiber. The width of the rectangular fiber is chosen to be slightly larger than the diode emitting area The height is as small as possible, typically around 30 to
Haake John M.
Pallett Thomas M.
Priest James A.
Zediker Mark S.
Magee John J.
Nuvonyx, Inc.
Sugarman Scott J.
LandOfFree
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